This invention pertains to lamp failure indicating circuits which are particularly useful in automotive vehicle applications for monitoring failure of headlamps, stop lamps, tail lamps, etc.
Various types of lamp failure indicating circuits have heretofore been proposed. Many of these can detect a failure only when a control switch for the lamp is turned on. In other words, these lamp failure indicating circuits cannot detect a failed lamp when the control switch is off. There are also other devices monitoring lamps such as light pipes. Light pipes suffer the same disadvantage as described above in that they cannot indicate a failed lamp when the control switch is off. Also the optic fibers constituting the light pipe are not inexpensive.
The present invention is directed to providing a new and improved lamp failure indicating circuit which can test for lamp failure regardless of whether the control switch for the lamp is on or off; which is cost effective and reliable; and which is particularly useful in automotive applications. The invention does not require the use of memory devices, but rather performs a continuous testing of a monitored lamp load regardless of whether the control switch which controls the lamp load is on or off.
The foregoing, along with additional features, advantages, and benefits of the invention, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose preferred embodiments of the present invention in accordance with the best mode contemplated at the present time for carrying out the invention.